Riveting method

ABSTRACT

A method of joining a plurality of sheets by means of a blind rivet, comprises:
     (i) forming holes in the sheets and placing the sheets together so that the holes are in register and form a single hole therethrough;   (ii) inserting a blind rivet into the hole formed in the sheets from a working side thereof, the blind rivet comprising a sleeve ( 1 ) positioned about a mandrel that has a head ( 4 ); and   (iii) setting the rivet.   

     The hole ( 24 ) is radially enlarged at the outwardly facing surface of at least the sheet on the blind side, and the sleeve of the rivet is deformed during setting to form a rivet joint in which no part of the rivet is proud of the outwardly facing surface ( 28 ) of the sheet at least on the blind side of the sheets. The method enables rivet joints to be formed in sheets, for example used in enclosures that house modules, where there is no space available for the set rivets to protrude.

This application is a divisional of U.S. patent application Ser. No.10/166,524, entitled “RIVETING METHOD”, filed Jun. 10, 2002, now U.S.Pat. No. 6,751,841.

BACKGROUND OF THE INVENTION

The present invention relates to methods of forming rivet joints.

Rivets and methods of joining metal sheets together employing rivetshave been known for many years, and involve inserting a rivet intoaligned holes drilled through the sheets followed by deforming the rivetby compression so that it expands radially on either side of the sheetsand holds them together. Where access to only one side of the sheets iseasily available, it is usual to employ a blind rivet for forming thejoint. A typical blind rivet comprises a sleeve formed from the rivetmaterial that is located about a mandrel having an enlarged head at oneend. Usually the mandrel extends some distance beyond the other end ofthe rivet sleeve as a pulling stem, and a radially extending flange isprovided on the end of the rivet sleeve opposite to the mandrel head. Inaddition, a point of weakness called a breakneck may be provided in themandrel in the region of the rivet sleeve. The blind rivet can beinserted through the hole formed in the sheets to be joined beginningwith the head of the mandrel until the flange on the rivet sleeve abutsthe surface of the sheet on the working side thereof so that only thehead of the mandrel and part of the rivet sleeve are located on theblind side of the sheets. The rivet can then be set by means of a rivetsetting tool which grasps the pulling stem of the rivet and pulls itaway from the proximal end of the rivet sleeve while applying a reactionforce to the flanged end of the sleeve. This causes the head of themandrel to be drawn toward the sleeve and the sleeve to be compressedbetween the head of the mandrel and the rivet setting tool. The settingtool will apply a sufficient force to deform the rivet sleeve axially,and therefore radially, so that the set rivet will hold the sheetstogether. After setting of the rivet, the mandrel may be snapped in twoat the breakneck and the remainder of the pulling stem can be discarded.The head of the mandrel and any part adjacent to it may be removed anddiscarded so that only the deformed rivet sleeve remains, although insome circumstances it may be left in the sleeve. Thus, in order to gripthe sheets and hold them together, some volume of rivet sleeve materialis required to remain on each outwardly directed surface of the metalsheets, this being provided by the flange on one side of the sheets.

This form of riveting has been considered for joining parts of thechassis or housing of an electronics assembly. Such a chassis or housingthat has been employed is in the form of a container formed from sheetmetal such as pressed aluminium zinc plated steel and having a number ofinternal, generally rectangular areas for receiving various components,for instances power modules, printed circuit boards, disc, tape andCD-ROM drives etc. Space is normally at a premium in such assemblies andvarious components will usually be inserted by sliding rectangularmodules into the appropriate recesses with no more than one or twomillimeters of tolerance. It is not economically feasible to join thevarious sheets forming the internal and external walls of the housing byspot welding because this would require re-plating of the steel sheetsafter welding. Also, it is not possible to employ usual rivets in suchan assembly because this would require access to both sides of thesheets to be joined by a relatively large “l” shaped anvil of a settingtool.

Accordingly it has been considered to employ blind rivets for joiningthe various metal sheets forming the chassis of the equipment. Howeverthe formation of protuberances on both surfaces of the sheets to bejoined by the rivets is not compatible with the requirement to be ableto slide the various components into and out of the chassis, nor is itcompatible with the proximity of various joined metal sheets forminginternal partitions or bulkheads to other parts of the chassis.

SUMMARY OF THE INVENTION

According to one aspect, the present invention provides a method ofjoining a plurality of sheets by means of a blind rivet, whichcomprises:

-   (i) forming holes in the sheets and placing the sheets together so    that the holes are in register and form a single hole therethrough;-   (ii) inserting a blind rivet into the hole formed in the sheets from    a working side thereof, the blind rivet comprising a sleeve    positioned about a mandrel that has a head; and-   (iii) setting the rivet;    wherein the hole is radially enlarged at the outwardly facing    surface of at least the sheet on the blind side, and the sleeve of    the rivet is deformed during setting to form a rivet joint in which    no part of the rivet is proud of the outwardly facing surface of the    sheets at least on the blind side of the sheets.

Thus, the method according to the invention has the advantage thataccess is only necessary to one side of the metal sheets to be joined(the working side) but that it is possible to form a rivet joint thatdoes not protrude on the other surface of the sheets that are joined(the blind side).

It is possible for the hole to be radially enlarged at the outwardlyfacing surfaces of both sheets and, after setting of the rivet, for nopart of the rivet to be proud of the outwardly facing surface of eithersheet.

The rivet sleeve may be shaped to engage the radial enlargement on theworking side of the hole, so that it performs a similar function to theflange on the sleeve of conventional blind rivets but does not extendbeyond the plane of the outwardly facing surface on the working side.This may be achieved by forming the sleeve with an enlarged part, forexample a part that tapers outwards in the form of a conical frustum(referred to herein as “frusto-conical”) and which engages the radialenlargement in the hole when the rivet is inserted into the hole.

Such a form of rivet is novel per se, and so, according to anotheraspect, the invention provides a blind rivet which comprises a hollowsleeve having an internal bore, and a mandrel that extends through thebore of the sleeve and has a head for supplying force to the sleeveduring setting of the rivet, wherein the sleeve has a substantiallyfrusto-conical portion at its end opposite to the head of the mandrelthat tapers radially outwards in a direction away from the head of themandrel.

The radial enlargement on either side of the sheets may have anyappropriate shape and need not necessarily be frusto-conical: it could,for example, be a generally cylindrical counterbore of larger diameterthan the hole so that the rivet sleeve would have one part of smallerdiameter that could extend through the hole and a second cylindricalpart of larger diameter. The invention will be described hereafter withreference to countersinking but it should be appreciated thatcounterbores or other enlargements may be employed.

Whatever the shape of the part of the rivet sleeve that engages thecountersink in the hole, the end surface of the rivet sleeve directedaway from the mandrel head is preferably flat so that, when the rivet isinserted into the hole, the end of the sleeve on the working side issubstantially flush with the surface of the sheet. It is possible ifdesired, and especially if manufacturing tolerances require, for thepart of the rivet sleeve that engages the countersink to be slightlyshorter than the depth of the countersink so that the rivet forms aslight depression in the joined metal sheets.

In an alternative form of rivet, the rivet sleeve may be substantiallycylindrical, and will stand proud of the surface of the sheet on theworking side when the rivet is inserted into the hole, and is deformedaxially and radially into the countersink during setting of the rivet.When the rivet sleeve has such a configuration, it should be appreciatedthat the sleeve itself has no means of ensuring correct axial locationwithin the hole, and so this must be provided by the setting tool. Inaddition, the setting tool should have a jaw that bears on the rivetsleeve itself and applies force on the rivet sleeve along the axis ofthe mandrel to deform the sleeve into the countersink.

The head of the mandrel may have any of a number of forms. In one formthe mandrel may have a region at the base of the head that slopes withrespect to the axis of the mandrel. In other words the head may bejoined to the rest of the mandrel by a frusto-conical portion. With thisconfiguration, when the rivet is set the head of the mandrel applies aradially outward force on the sleeve in addition to an axial force andthereby causes the sleeve to expand radially into the countersink on theblind side of the metal sheets. The shape of the mandrel head in thiscase will depend on whether or not the mandrel is discarded aftersetting the rivet. For example, the mandrel head may have a generallyflat end surface so that it can be flush with the surface of the sheeton the blind side, in which case it may remain in the rivet aftersetting if desired or it can be removed.

Alternatively, the mandrel head may have a generally radially extendingshoulder portion or shoulder where the head meets the shank of themandrel so that the rivet sleeve is caused to deform axially duringsetting of the rivet. Such a mandrel will necessarily have a domed headwhich, although could be flush with the surface of the sheets on theblind side, will normally remain proud of the surface and so should beremoved after setting of the rivet.

According to a further aspect, the invention provides a rivet joint thatis formed between a plurality of sheets that have been placed togetherand have a hole extending therethrough, wherein the hole is radiallyenlarged at the outwardly directed surface of the at least one sheet andthe rivet joint is formed by means of a rivet sleeve that extends intothe or each radial enlargement but does not protrude above the outwardlydirected surfaces of the sheet at the radial enlargement of the hole.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings, in which correspondingparts are given like reference numbers. In the drawings:

FIG. 1 is a sectional elevation of a conventional blind rivet;

FIG. 2 is a sectional elevation of the conventional rivet during settingthereof;

FIG. 3 is a sectional elevation of the conventional rivet after settingthereof;

FIG. 4 is a sectional elevation of a blind rivet used in the methodaccording to the present invention;

FIG. 5 is a sectional elevation of the rivet of FIG. 4 inserted in placein a workpiece;

FIG. 6 is a section through a set rivet joint formed by the rivet ofFIG. 4;

FIG. 7 is a sectional elevation of an alternative form of rivet used inthe method according to the invention;

FIG. 8 is a sectional elevation of the rivet of FIG. 7 during setting;

FIG. 9 is a section through the set rivet joint formed by the rivet ofFIG. 4;

FIG. 10 is a sectional elevation of another alternative form of rivetused in the method according to the invention;

FIG. 11 is a section through a set rivet joint using the rivet of FIG.10;

FIG. 12A and FIG. 12B are sections through yet another form of rivetjoint according to the invention before and after setting; and

FIG. 13 is a perspective view showing part of an electronics chassisemploying such rivet joints.

DESCRIPTION OF PARTICULAR EMBODIMENTS

Referring now to the drawings, in which like reference numerals are usedto designate corresponding elements, FIG. 1 shows a conventional form ofblind rivet. The rivet comprises a hollow sleeve 1 having a throughborefor receiving a mandrel 2 that extends through it and terminates at oneend in a head 4. At its other end the mandrel extends beyond the end ofthe sleeve 2 and becomes a pulling stem 6 that can be gripped by a rivetsetting tool. At the end opposite the mandrel head 4, the sleeve 1 has aradially extending flange 8 having a flat inwardly facing surface 10 anda slightly domed outwardly facing surface 12.

In operation, in order to form a rivet joint between metal sheets 14 and16, the rivet is inserted into a hole that has been drilled through thesheets starting with the head 4 of the mandrel until the surface 10 ofthe flange 8 abuts the outwardly facing surface of the sheet 16. Therivet is then set by means of a setting tool having a pair of jaws 18and 20. One of the jaws, jaw 20, grips the pulling stem 6 while theother jaw abuts the outwardly facing surface 12 of the flange. As thesetting tool is operated, the jaws 18 and 20 move apart as shown by thearrows in FIG. 2, which causes the rivet sleeve to be axially compressedbetween the head 4 of the mandrel and the flange 12 on the sleeve andalso to expand radially. After setting of the rivet, the pulling stemcan be snapped off the rest of the mandrel at a point of weakness (notshown) also called a breakneck, and both parts of the mandrel can bediscarded to leave a rivet connection as shown in FIG. 3.

The standard rivet has the drawback that the rivet joint so formed has aprotuberance on each side, one protuberance being formed by the flange 8of the rivet sleeve and the other being formed by the deformed oppositeend of the rivet sleeve.

One method of forming a rivet joint according to the present inventionin which a joint that is flush with the outer surfaces of the joinedsheets is shown in FIGS. 4 to 6. A blind rivet that can be used in themethod has a conventional mandrel 2 with a head at one end and forming apulling stem at the other end. The rivet sleeve 1 has a generallycylindrical part at one end adjacent to the mandrel head 4 of an outerdiameter generally equal to that of the mandrel head. At the other end,the sleeve has a frusto-conical part 22 that extends axially overapproximately half the length of the sleeve and which tapers radiallyoutwards in a direction away from the head of the mandrel.

In order to form a rivet joint a hole is formed in each sheet to bejoined, but instead of a hole having a constant bore, the holes arecountersunk so that each sheet 14 and 16 has a countersink 24 and 26that is frusto-conical in shape, expanding radially toward the outwardlyoriented surface 28 and 30 of each sheet. The angle of the countersinksurfaces is about 120° to an axis normal to the plane of the sheets andthe hole diameter increases along each countersink from 3.3 mm to 6.3mm. The frusto-conical part 22 of the rivet sleeve has approximately thesame dimensions as the countersink in sheet 30 so that the rivet can beinserted into the hole formed in the sheets from the working side andthe frusto-conical part 22 of the sleeve will seat itself in thecountersink 26 with outwardly directed surface 32 flush with the surface30 of sheet 16 as shown in FIG. 5. The rivet can then be set in the samemanner as with a conventional rivet so that the cylindrical end of thesleeve 1 is axially squashed by the mandrel head and is deformedradially outwardly into the countersink 24 on the blind side of sheet14. After setting the rivet, the mandrel 2 may be snapped at itsbreakneck and the parts thereof removed to produce a rivet joint asshown in FIG. 6. If the size of the cylindrical part of the rivet sleeve1 is appropriately chosen i.e. so that its volume is less than thevolume of the countersink 24 in sheet 14 (after subtracting the volumeof that part of the mandrel 2 that passes through the countersink 24from the volume of the countersink) and for example not more than 80%thereof, it is possible to form a rivet joint in which no part of therivet protrudes above the outwardly oriented surfaces 28 and 30 of thesheets.

An alternative riveting method is shown in FIGS. 7 to 9. In this methoda rivet similar to a conventional rivet is used but without a flange 8on the rivet sleeve. In order to form a rivet joint, the rivet isinserted into a hole formed in the sheets 14 and 16 that have outwardlyfacing countersinks as described above, and the rivet is set as beforeby means of a rivet setting tool as shown in FIG. 8 so that the sleeve 1is axially deformed under a compressive force between the head 4 of themandrel and the jaw 18 of the rivet setting tool. In this method, bothends of the rivet sleeve are caused to deform axially and expandradially to form a rivet joint as shown in FIG. 9 after the mandrel 2has been broken and removed. In this method, however, no element on therivet sleeve 1 can ensure correct seating of the rivet sleeve in thecountersink 26 and so another arrangement, for example provided on thesetting tool, must be provided in order to ensure correct location ofthe rivet sleeve 1 within the hole.

As in the form of rivet shown in FIGS. 4 to 6, if the size of rivetsleeve is chosen so that the volume thereof extending within and beyondeach countersink 24 and 26 is less than the volume of the countersinkafter subtracting the volume of that part of the mandrel that passesthrough each countersink from the volume of the countersink, for examplenot more than 80% thereof, a flush rivet joint may be obtained.

Another alternative method of forming a rivet joint according to theinvention is shown in FIGS. 10 and 11. The rivet that is employed inthis method is generally similar to the rivet shown in FIG. 4, andcomprises a hollow rivet sleeve 1 through which a mandrel 2 extends witha head 4 at the end and forming a pulling stem at the other. The end ofthe sleeve 1 opposite to the mandrel head 4 has a frusto-conical form 22in which its radius increases in a direction away from the mandrel head4.

In this design of rivet, the mandrel head 4 has a relatively flat uppersurface 34 and a frusto-conical part 36 that joins the flat uppersurface of the shank of the mandrel 2.

When the rivet is set, by pulling the pulling stem 6 of the mandrel, thefrusto-conical part 36 of the head will deform the upper part of thesleeve 1 radially outwardly into the countersink 24 as it enters thebore of the sleeve 1. After setting, the mandrel 2 may be broken bysnapping it at a breakneck and the pulling stem discarded. The head ofthe mandrel may also be discarded to leave a rivet joint as shown inFIG. 11, or, because the head 4 has a flat upper surface, it may bepossible to leave the mandrel head in place without it being proud ofthe outwardly oriented surface 28 of sheet 14.

As shown in the Figures, the countersinks in the sheets 14 and 16 extendthrough substantially the entire thickness of the sheets. This is not,however, necessary and the sheets may, for example, be provided withcylindrical holes that are counterbored only over part of their depth.

FIGS. 12A and 12B show a further form of rivet joint that may be formedby the method according to the present invention. In this method a rivetsimilar to a conventional rivet is employed having a rivet sleeve 1 witha flange 8, and a mandrel 2 ending in a pulling stem 6. The hole drilledthrough the sheet 16 on the working side is cylindrical while the holeformed in the sheet on the blind side is provided with a countersink 24.The rivet joint is formed by passing the blind rivet through the hole inthe sheets 14 and 16 until the flange 8 abuts the surface of sheet 16 onthe working side, and then the rivet is set by pulling the pulling stemaway from the flange 8 and then breaking the mandrel head off themandrel. When the rivet is set, the rivet will be proud of the surfaceof sheet 16 on the working side, but will not protrude above theoutwardly facing surface 28 of the sheet 14 on the blind side. Thismethod is useful where space on the working side of the rivet permitssome degree of height but no height of the rivet can be tolerated on theblind side thereof.

FIG. 13 shows part of the chassis for electronics equipment in whichrivet joints formed in accordance with the present invention may beemployed. The chassis has one part 40, for example, that contains anumber of modules 42 that are inserted therein and slid to its correctposition, in the direction of the arrow, and another part 44 that cancontain other modules 45 and is separated therefrom by a partition orbulkhead 46. As shown, one partition has a flange 48 that is butted upto the bulkhead 46 and is joined thereto according to the presentinvention by means of flush rivets 50. In this form of assembly it isimportant that the rivets 50 do not protrude into space 40 or they wouldobstruct insertion of modules 42 therein, while no space exists betweenthe sheet forming the partition 46 and the module 45 for a proud rivet.In addition, due to the depth of the parts 40 that contain the modulesand their lateral dimensions, it is not possible to locate equipment forforming any riveted joint other than a blind riveted joint.

The scope of the present disclosure includes any novel feature orcombination of features disclosed therein either explicitly orimplicitly or any generalisation thereof irrespective of whether or notit relates to the claimed invention or mitigates any or all of theproblems addressed by the present invention. The applicant hereby givesnotice that new claims can be formulated to such features during theprosecution of this application or of any such further applicationderived therefrom. In particular, with reference to the appended claims,features from dependent claims can be combined with those of theindependent claims and features from respective independent claims canbe combined in any appropriate manner and not merely in the specificcombinations enumerated in the claims.

1. A rivet joint that has been formed between a plurality of sheets by amethod which comprises: (i) forming holes in the sheets and placing thesheets together so that the holes are in register and form a single holetherethrough; (ii) inserting a blind rivet into the hole formed in thesheets from a working side thereof, the blind rivet comprising a sleevepositioned about a mandrel that has a head; and (iii) setting the rivet;wherein the hole is radially enlarged at the outwardly facing surface ofat least the sheet on the blind side, and the sleeve of the rivet isdeformed during setting to form a rivet joint in which no part of therivet is proud of the outwardly facing surface of the sheet at least onthe blind side of the sheets.
 2. A joint as claimed in claim 1, whereinthe hole is radially enlarged at the outwardly facing surfaces of bothsheets and after setting of the rivet, no part of the rivet is proud ofthe outwardly facing surface of either sheet.
 3. A joint as claimed inclaim 2, wherein the rivet sleeve is shaped to engage the radialenlargement on the working side of the hole.
 4. A joint as claimed inclaim 3, wherein the rivet sleeve has a substantially frusto-conicalpart that engages the radial enlargement on the working side of the holewhen the rivet is inserted in the hole.
 5. A joint as claimed in claim4, wherein the frusto-conical part of the sleeve has a flat end surfacethat is substantially flush with the surface of the sheet on the workingside thereof.
 6. A joint as claimed in claim 2, wherein the rivet sleeveis substantially cylindrical and is deformed into the countersink on theworking side of the sheets during setting thereof.
 7. A joint as claimedin claim 6, wherein, during setting of the rivet, a setting tool jawapplies force on the rivet sleeve along the axis of the mandrel todeform the sleeve into the countersink.
 8. A joint as claimed in claim1, wherein the mandrel has a region at the base of the head that slopeswith respect to the axis of the mandrel so that, during setting of therivet, part of the sleeve is deformed radially outwardly into thecountersink on the blind side of the sheets.
 9. A joint as claimed inclaim 8, wherein the mandrel head has a generally flat upper surface andremains in the rivet sleeve in the rivet joint.
 10. A joint as claimedin claim 1, wherein the mandrel head has a generally flat lower portionwhich causes the rivet sleeve to deform axially during setting of therivet.
 11. A joint as claimed in claim 1, wherein the mandrel has beenremoved from the rivet joint after setting.
 12. A housing forelectronics equipment that contains one or more rivet joints as claimedin claim 1.